1. Field of the Invention
This invention relates generally to semiconductor device manufacturing, and, more particularly, to a method and apparatus for monitoring consumable performance in a processing tool.
2. Description of the Related Art
The manufacture of most devices, such as semiconductor devices, requires a number of discrete processing steps to create the device. With respect to semiconductor devices, a number of discrete steps are needed to produce a packaged semiconductor circuit device from raw semiconductor material. The starting substrate is usually a slice of single crystal silicon referred to as a wafer. Circuits of a particular type are fabricated together in batches of wafers called xe2x80x9clotsxe2x80x9d or xe2x80x9crunsxe2x80x9d. The fabrication process creates regular arrays of a circuit on the wafers of a lot. During processing, the individual wafers in a lot may go through individual processing steps one at a time or as a batch. At the completion of wafer processing, the wafers are tested to determine circuit functionality. Later, the wafers are cut to separated the individual integrated circuit devices, the functioning devices are packaged, and further testing is performed prior to use by the customer.
Various processing tools used in the production of the semiconductor devices employ consumable items that are gradually depleted over their service lives. This depletion affects the performance of the tool in which they are employed. Often, periodic adjustments to the operating recipes of the tools are required to compensate for the degraded performance of the tool. Generally, these adjustments increase the time required to process the wafers in the tool.
One particular tool employing consumable items is a chemical mechanical polishing (CMP) tool. In a CMP process, the upper surface of a layer previously formed on a wafer is planarized to ease formation of subsequent process layers. Chemical mechanical polishing typically uses an abrasive slurry disbursed in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action. Generally, a CMP tool includes a polishing device positioned above a rotatable circular platen or table on which a polishing pad is mounted. The polishing device may include one or more rotating carrier heads to which wafers may be secured, typically through the use of vacuum pressure. In use, the platen may be rotated and an abrasive slurry may be disbursed onto the polishing pad. Once the slurry has been applied to the polishing pad, a downward force may be applied to each rotating carrier head to press the attached wafer against the polishing pad. As the wafer is pressed against the polishing pad, the surface of the wafer is mechanically and chemically polished. Both the polishing pad and the carrier heads are subject to gradual deterioration. This degradation gradually decreases the polishing rate of the CMP tool over the life of the pad and carriers. Eventually, a polishing pad may fail catastrophically and cease to polish entirely. To respond to this degradation, certain process parameters may be modified. For example, the polishing time parameter in the operating recipe of the CMP tool must be periodically increased over time. Additionally, the down force applied by the carrier heads may be varied. After a predetermined number of wafers have been polished or after a specified time interval, the polishing pad and/or carrier heads are replaced.
Another exemplary tool employing consumable resources is a sputtering deposition tool. A sputtering tool uses a metal source, commonly referred to as a target, and bombards the source with energized ions, causing particles of the metal to be displaced and deposited on the surface. Over time, characteristics of the target, such as surface porosity, change due to the repeated physical bombardment. As a result the deposition rate decreases over time, and the operating recipe of the sputtering tool is periodically updated to increase the deposition time over the life of the target. Generally, sputtering targets are replaced on fixed intervals, such as after processing a predetermined number of wafers. The actual degradation rate experienced by individual targets may vary. Replacement intervals are generally selected to account for nearly the worst case degradation rate. As a result, certain targets are replaced before their useful life has been exhausted. Certain sputtering targets, such as gold, are costly. Premature retiring of such expensive targets is inefficient. On the other hand, as the deposition time is increased to account for the degradation in the target, there may come a point where the deposition time in the sputtering tool affects the overall critical path of wafers in the processing line. At such a point, the costs saved by keeping the target in service may be negated by the costs incurred as a result of delays in the processing line. Additionally, with very long replacement intervals, the entire target can be depleted in places and require immediate replacement to maintain the quality and composition of the deposited metal. The use of a fixed replacement interval attempts to find a compromise balancing these concerns.
In both exemplary cases described above, and in others not mentioned, the performance of the consumable items affect the operation of the individual processing tool as well as the efficiency of the processing line in which they participate. The use of fixed replacement intervals for consumable items is not always an effective solution for optimizing tool and line efficiency.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a method for monitoring consumable performance in a processing tool. The method comprises storing a performance model of the processing tool; receiving a consumable item characteristic of a consumable item in the processing tool; determining a predicted processing rate for the processing tool based on the consumable item characteristic and the performance model; determining an actual processing rate of the processing tool; and determining a replacement interval for the consumable item based on at least the actual processing rate.
Another aspect of the present invention is seen in a processing system including a processing tool and an automatic process controller. The processing tool is adapted to process wafers and includes a consumable item. The automatic process controller is adapted to store a performance model of the processing tool, receive a consumable item characteristic of the consumable item in the processing tool, determine a predicted processing rate for the processing tool based on the consumable item characteristic and the performance model, determine an actual processing rate of the processing tool, and determine a replacement interval for the consumable item based on at least the actual processing rate.